US7583783B2 - X-ray computer tomograph and method for examining a test piece using an x-ray computer tomograph - Google Patents

X-ray computer tomograph and method for examining a test piece using an x-ray computer tomograph Download PDF

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Publication number
US7583783B2
US7583783B2 US11/625,429 US62542907A US7583783B2 US 7583783 B2 US7583783 B2 US 7583783B2 US 62542907 A US62542907 A US 62542907A US 7583783 B2 US7583783 B2 US 7583783B2
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detector array
detector
ray
computer tomograph
radiation
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US11/625,429
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US20070153970A1 (en
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Geoffrey Harding
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Yxlon International Security GmbH
Smiths Detection Inc
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GE Homeland Protection Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • G01N23/046—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material using tomography, e.g. computed tomography [CT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/20—Sources of radiation
    • G01N2223/201—Sources of radiation betatron
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/40—Imaging
    • G01N2223/419—Imaging computed tomograph

Definitions

  • the invention concerns an x-ray computer tomograph, having an x-ray source that generates a fan beam and having a two-dimensional energy-resolving detector array, both of which are situated on a gantry.
  • the invention also concerns a method for examining a test piece using an x-ray computer tomograph.
  • DE 10 009,285 A1 has disclosed a computer tomograph for detecting the pulse transmission spectrum in a test region.
  • an x-ray source equipped with a primary collimator is situated on a gantry that can be rotated around one axis and generates a fan beam.
  • a detector array is provided, which is likewise attached to the gantry and is used for detecting the x-rays passing through a test region.
  • a secondary collimator which only permits x radiation from a certain scattering voxel in the test region to pass through to an associated column of the detector array, Based on the scattered data obtained and the measured primary radiation in the plane of the fan beam, an iterative algebraic reconstruction technique (ART) is used to execute a reconstruction for each scattering voxel in the test region through which a primary beam passes, in conjunction with the pulse transmission spectrum.
  • the pulse transmission spectrum is characteristic of the material in the relevant scattering voxel and thus provides information about its physical composition.
  • a computer tomograph of this kind and the method executed with it both suffer from significant disadvantages.
  • the computer tomograph is rendered significantly more expensive by the use of a secondary collimator.
  • the leakage flux is reduced since part of the scattered x-ray quanta is absorbed at the secondary collimator, thus requiring a higher tube output or a longer testing time.
  • the secondary collimator itself constitutes a scattering source so that particularly with increasing photon energy, “smearing effects” occur in the measured pulse transmission spectrum.
  • the object of the invention is to overcome the above-mentioned disadvantages.
  • the object is obtained by means of an x-ray computer tomograph with the defining characteristics of claim 1 .
  • an x-ray computer tomograph according to the invention is also less expensive than its prior counterpart equipped with a secondary collimator since on the one hand, material costs can be saved and on the other hand, the gantry is required to move significantly less mass during its rotation, which permits the use of less expensive drive units and bearings.
  • the pulse transmission spectrum lies between 0.2 and 2 nm ⁇ 1 .
  • the peak data and the intensity of the molecular structure functions for these materials are negligible above this range.
  • the energy of the x radiation lies between 100 and 500 keV. Such a high-energy x radiation broadens the testing region, both in security checks and in nondestructive analysis. In addition, this energy also has a positive impact on the required size of the individual detector elements of the detector array.
  • the detector array is situated on a circumference surface of a cylinder around a center axis extending through the x-ray source, perpendicular to the fan beam.
  • the detector resolution thus produced achieves an acceptable detector element height at very high x-ray energies and a conventional distance of the measuring point from the detector. It is advantageous if a pixelated detector array is used as the detector array, which is equipped with from 5 to 50 detector elements in the direction of the y axis. preferably 15 detector elements.
  • the object is also attained by means of a method with the defining characteristics of claim 7 .
  • a locally resolved measurement of coherent x radiation scattered forward by the test piece is performed without a secondary collimator being positioned between the test piece and the detector array.
  • carrying out the method according to the invention yields the same advantages that have already been described above in relation to the x-ray computer tomograph according to the invention.
  • the gantry in order to record the scattered data, is rotated around an axis that is perpendicular to the plane of the fan beam. If scattered radiation from other scattering voxels strikes a detector element during an exposure without rotation of the gantry, then this is compensated for by the rotation since this causes a continuous succession of different partial beams to pass through the scattering voxel.
  • the scattered radiation coming from the scattering voxel thus changes constantly, enabling a deduction based on the large amount of data that are obtained during the rotation of the gantry.
  • FIG. 1 is a perspective, schematic view of an x-ray computer tomograph according to the invention.
  • FIG. 2 is a view to perpendicular to the fan beam of the x-ray computer tomograph from FIG. 1 .
  • FIG. 1 shows the schematic design of an x-ray computer tomograph according to the invention in a very simplified fashion.
  • a fan beam 2 is used, which is produced by an x-ray source 1 .
  • the fan beam 2 is usually generated by means of a slit diaphragm serving as a primary collimator (not shown).
  • the beam passes completely through the entire width of the test piece 4 .
  • a secondary collimator is positioned between the test piece 4 and a detector array 5 and only permits scattered radiation from a certain region of the test piece 4 , i.e.
  • the scattering voxel S to strike a certain element of the detector array 5 .
  • the molecular structure functions of the materials that are of interest in the field of security only lie in a range of pulse transmission q max of 0.2 to 2 nm ⁇ 1 .
  • q max 0.2 to 2 nm ⁇ 1 .
  • ⁇ corresponds to an energy of the x-ray quanta of approximately 500 keV. This means that the electrons producing the x-ray quanta must be in the relativistic range since their static energy E 0 is 511 keV.
  • E 0 the static energy indicated
  • the main portion of the scattered signal from a scattering voxel S stems from the line of sight 3 between the detector element and the x-ray source 1 .
  • the contribution to coherent scattering of a material from a scattering voxel S situated on the line of sight 3 of an adjacent detector element is negligibly small. For this reason, it is no longer necessary to insert a secondary collimator equipped with leaves between the test piece 4 and the detector array 5 .
  • the detector array 5 has a series of elements in a two-dimensional structure. It is manufactured out a material that has the capacity for energy-resolving detection, for example CdZnTe.
  • the detector elements of the detector array 5 are situated on a circumference surface of a cylinder.
  • the axis of the cylinder circumference passes through the x-ray source 1 and extends parallel to the y axis, i.e. perpendicular to the fan beam 2 .
  • the dashed line indicates the Z axis, which in the instance shown. corresponds to the line of sight 3 between the detector element—which is situated at the coordinate origin—and the x-ray source 1 .
  • the detector array 5 has rows that extend parallel to the x axis and columns that extend parallel to the y axis,
  • the primary radiation elements 6 are situated on the x axis and are used to detect x radiation coming directly from the x-ray source 1 and passing through the test piece 4 , i.e. radiation that has not been scattered.
  • the width B of a “strip” an object that emits coherent scattered radiation into a particular detector column is ⁇ Z P * ⁇
  • this fulfills the condition according to the invention for the spatial resolution of the detector elements in their width B in the x direction, making it possible to eliminate a secondary collimator.
  • the whole detector array 5 extends far enough in the x direction to detect the entire fan beam 2 passing through the test piece 4 .
  • 50 detector elements are usually sufficient since the coherent scattered radiation decreases in intensity as scattering angles increase,
  • the coherently scattered x radiation from a scattering voxel S around a certain observation point P causes significant scattered radiation to be detected only in the above-indicated scattering angle range of up to ⁇ .
  • the radius R of this region is proportional to the product ⁇ *Z P for small angles, where Z P represents the coordinates of the observation point P in relation to the origin of the coordinate system, Based on known x-ray computer tomographs, this distance Z P is assumed to be approximately 2 m, thus yielding a radius R of approximately 1 cm.
  • the detector resolution depends on this radius RP The more detector elements in a column of the detector array 5 are situated within this radius A, the finer resolution is.
  • the detector resolution achieved is R/N, where N must be greater than 10 in order to obtain reasonable results. Good results are obtained for N between 10 and 50; preferably N is selected to be equal to 15.
  • the only material that contributes to the coherent scattered signal in a specific detector element is that which is situated in the region of the scattering voxel S.
  • Simulation calculations have established that although a multitude of different contributors do in fact contribute to the overall scattered signal, in the range of low pulse transmissions q, the coherent scattering predominates. This is because electron-binding effects suppress the single Compton signal, while the multiple Compton signals constitute a structureless background that can often be approximated by means of a constant.
  • FIG. 2 schematically depicts how the x-ray source 1 and the detector array 5 are attached to a gantry (not shown) that can be rotated around the test piece 4 .
  • the region of the test piece 4 that an individual detector element of the detector array 5 “sees” is clearly visible in this figure.
  • the gantry is rotated by an imaging angle ⁇ around an axis parallel to the y axis.
  • the detector array 5 takes a reading for each value of the imaging angle ⁇ so that for each imaging angle X, a four-dimensional data set is generated, In addition to the imaging angle ⁇ .
  • This data set S raw ( ⁇ ,E, x, y) [depends] also on the energy E of the x-ray quantum that is detected in the energy-resolving detector element as well as the x and y coordinates of the detector element that performs the detection.
  • the section below will describe a method with which the four-dimensional scattered data obtained can be used to deduce what material is contained in the test piece 4 at each individual scattering voxel S.
  • an energy calibration must be performed on the system. This is followed by the subtraction of the multiple scattering components from the scattered signal detected. Then the scattered signal is scaled to the transmission component. Based on the above-mentioned raw data S raw , this yields the corrected scattered data S ( ⁇ , E, x, y) of the scattered signal.
  • Such methods are known from the literature and are referred to as algebraic reconstruction techniques (ART).
  • the second step requires an estimation of the multiple scattering component. This can be derived from measurements or photon transport simulations with typical test piece geometries. It is also possible to formulate this second step in the iterative construction by estimating the multiple scattering component, which is based on the current object distribution. In ART, forward projection data that result from an assumed material distribution with a known molecular structure function are compared to the measured scattered data. The deviations between these two data sets are subjected to iterative back projections into the object space.
  • Data of the back projection of the data S ( ⁇ 1 , E 1 , x 1 , y 1 ) from the first projection into the object space are inserted into an object matrix ⁇ mol , taking into account the geometric assumptions.
  • the rotation of the system comprised of the x-ray source 1 and detector array 5 is simulated, with the angular steps that were executed during the measurement.
  • a forward projection is then performed using the values of the object matrix ⁇ mol from the first step,
  • the difference between the forward projection data and the measured data is inserted into a difference matrix that is then used for a back projection.
  • Repeated iterative forward and back projections are performed until the imaging data have all been used once, This procedure is repeated several times, with the weighting being reduced each time until the average quadratic error sum of the difference matrix is no longer reduced in the subsequent iteration step.

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  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Pulmonology (AREA)
  • Radiology & Medical Imaging (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
US11/625,429 2004-07-23 2007-01-22 X-ray computer tomograph and method for examining a test piece using an x-ray computer tomograph Expired - Fee Related US7583783B2 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE102004035943.1 2004-07-23
DE102004035943A DE102004035943B4 (de) 2004-07-23 2004-07-23 Röntgencomputertomograph sowie Verfahren zur Untersuchung eines Prüfteils mit einem Röntgencomputertomographen
PCT/EP2005/008082 WO2006010588A2 (fr) 2004-07-23 2005-07-25 Tomographe a rayons x assiste par ordinateur ainsi que procede pour examiner une piece a controler a l'aide d'un tomographe a rayons x assiste par ordinateur
EPPCT/EP05/08082 2005-07-25

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US7583783B2 true US7583783B2 (en) 2009-09-01

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EP (1) EP1774301A2 (fr)
CN (1) CN101088007A (fr)
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WO (1) WO2006010588A2 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9335281B2 (en) 2011-10-07 2016-05-10 Duke University Apparatus for coded aperture X-ray scatter imaging and method therefor
US20160170075A1 (en) * 2013-07-25 2016-06-16 Analogic Corporation Generation of diffraction signature of item within object
US10004464B2 (en) 2013-01-31 2018-06-26 Duke University System for improved compressive tomography and method therefor
US10107768B2 (en) 2013-08-13 2018-10-23 Duke University Volumetric-molecular-imaging system and method therefor
US10987071B2 (en) * 2017-06-29 2021-04-27 University Of Delaware Pixelated K-edge coded aperture system for compressive spectral X-ray imaging
US11181489B2 (en) * 2018-07-31 2021-11-23 Lam Research Corporation Determining tilt angle in patterned arrays of high aspect-ratio structures by small-angle x-ray scattering

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Publication number Priority date Publication date Assignee Title
US8000435B2 (en) * 2006-06-22 2011-08-16 Koninklijke Philips Electronics N.V. Method and system for error compensation
DE102009036579A1 (de) * 2009-08-07 2011-02-17 Wenzel Volumetrik Gmbh Röntgendetektorvorrichtung
RU2016137605A (ru) * 2014-06-16 2018-03-28 Конинклейке Филипс Н.В. Гибридное получение данных в компьютерной томографии (кт)
US10789738B2 (en) * 2017-11-03 2020-09-29 The University Of Chicago Method and apparatus to reduce artifacts in a computed-tomography (CT) image by iterative reconstruction (IR) using a cost function with a de-emphasis operator
CN113552640A (zh) * 2020-04-02 2021-10-26 同方威视技术股份有限公司 射线检查系统及散射校正方法

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9335281B2 (en) 2011-10-07 2016-05-10 Duke University Apparatus for coded aperture X-ray scatter imaging and method therefor
US10004464B2 (en) 2013-01-31 2018-06-26 Duke University System for improved compressive tomography and method therefor
US20160170075A1 (en) * 2013-07-25 2016-06-16 Analogic Corporation Generation of diffraction signature of item within object
US10261212B2 (en) * 2013-07-25 2019-04-16 Analogic Corporation Generation of diffraction signature of item within object
US10107768B2 (en) 2013-08-13 2018-10-23 Duke University Volumetric-molecular-imaging system and method therefor
US10987071B2 (en) * 2017-06-29 2021-04-27 University Of Delaware Pixelated K-edge coded aperture system for compressive spectral X-ray imaging
US11181489B2 (en) * 2018-07-31 2021-11-23 Lam Research Corporation Determining tilt angle in patterned arrays of high aspect-ratio structures by small-angle x-ray scattering

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DE102004035943B4 (de) 2007-11-08
CN101088007A (zh) 2007-12-12
US20070153970A1 (en) 2007-07-05
WO2006010588A2 (fr) 2006-02-02
EP1774301A2 (fr) 2007-04-18
WO2006010588A3 (fr) 2006-03-30
DE102004035943A1 (de) 2006-02-16

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